A conventional pressure flush system uses a pressure water vessel disposed inside a toilet water tank. When water is infused into the vessel, the air in the water vessel is compressed and pressure accumulates inside the vessel. When a flush is needed, a user discharges the pressurized water through a discharge valve and through a toilet bowl trapway in order to provide a flushing action.
Thus, a pressure flush system utilizes compressed air to drive water into the bowl instead of the “pulling” or siphon action of gravity style toilets. As the result, a little amount of water provides a full and effective flushing of the pressure flush toilet.
The typical structure of a prior art pressure flush system is described in patent to Martin, 1977 (No.4233698), which primarily includes the pressure water vessel, flush valve, control valve refill valve, and air induction valve used to add pressure to the flush valve. In such a system, however, there are some problems as follows:                1. The flush valve of the system has only one single flush function. That is to say that once the control valve opens the flush valve, all volume of water in the water vessel will be flush out. Under this method the adjustment of discharge volume is not allowed.        2. There is only one secure device taken in the air induction valve. Since the water vessel is sealed, pressure must be contained. Any excess pressure over the strictly preset limitation may be dangerous. Therefore, there is potential safety concern if there was only one discharge protector used.        3. The refill rate is not adjustable. The refill volume may be too much or too little when the system is used with differently designed toilet bowls.        4. The flush valve cannot be shut off when a low pressure occurs in the water supply pipe, and this may cause water leaking from the pressure vessel.        
Another prior art example is the reissued patent Martin et al., 2002 (NO.RE37921E7), which comprises a water vessel, an external manifold mounted directly on said vessel, and an internally mounted flush valve assembly. The manifold comprises a water pressure regulator, an air induction system, and a manually operable flush valve actuator. The manually operable flush valve actuator controls the discharge of water under pressure from the water vessel into the toilet bowl. Although some improvements were made in this invention, there are still some shortcomings as follows:                1. The system only has the single flush function also and the refill rate is not adjustable.        2. A complicated cleaning device is required. To make the piston of the flush valve drop slowly enough to make the pressure water let out from the vessel completely, the annular section of the inlet of the flush valves must be as small as about 0.00078 inch2 or 0.5 mm 2). A small opening like this is very easy to be blocked by impurities in the water supply. Therefore, a cleaning device needs to be attached, which complicates the structure.        
Other partial flush systems have been implemented, but have not been implemented with a pressurized flushing system. The term partial flush refers to quantities that are less than a full flush. The term partial flush is not limited to fifty percent water volume of a full flush.